It's also helpful to maybe accept that you were equally responsible for the things that happened to you. It's so easy to point the finger and say how awful, manipulative and a jerk he was. At the same time though, he didn't exactly put a gun to your head did he? You knew it was wrong to continue to see him after you initiated the break up, you just felt too attached and couldn't let go. It's a learning experience and I think you certainly know better for the future. You cannot change what has happened but you should be a stronger and wiser person for experiencing it first hand. Other girls are sadly going to find out the hard way like you did but that's not your problem.
Knowing that he is with somebody else obviously indicates you are keeping tabs on him. Stop doing that. Remove him from facebook and if you guys, god forbid, still talk, don't. You need this time on your own to get yourself back on track here. And it won't if constant reminders of him are still in your face every day.
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.